text:
Is there any disadvantage to having the de-icing system on?
I was watching Mayday S11E02 about West Caribbean airways flight 708 and the pilots turned off the de-icing system partway through the flight. It's not why it crashed, but I was curious as to if there was any disadvantage to having the de-icing system on.

There are many components to the de-icing system. Do you specifically mean the wings? For wings there's both de-icing boots (only used when there's build-up) and surface de-icing. There's also probe (pitot and AOA) heat (always on), and in props, prop heat (in visible moister), and some have induction icing protection. There's also windshield de-ice. You'll need to be more specific about what kind of anti-ice you mean.

The wikipedia article already linked in the question says:

The system uses power from the engines, thus reducing their maximum performance. With the anti-ice system on, the highest altitude at which the overloaded aircraft could fly – without stalling – was reduced to 31,900 feet (9,700 m).

The de-icing system on most turbine aircraft (including MD-82 involved in that accident) uses bleed air from the engines, that is it extracts some air from behind the (low pressure stage of the) compressor. This air is therefore not ejected from the nozzle and not producing thrust, so the thrust is reduced. Or fuel flow rate increased if thrust levers are advanced to compensate, provided the engines are still below their maximum permitted thrust setting. Either way fuel consumption per mile increases.
Compressing air increases it's temperature, so this pressurized air is simply blown through tubes under the critical surfaces. There are other uses of bleed air, mainly pressurization and air-conditioning, but turning on deicing increases it's consumption significantly.
And note that this switching de-icing off and on was part of the accident sequence. It was only because they turned de-icing off that they were able to climb to FL330 in the first place.
It is also often not allowed to use de-icing when outside temperature is higher than some value because the heated surfaces could overheat.

non-fuel injected R-44s lose 1.6" MP with full carb heat.

@rbp: That's piston engine though; turbines don't have manifold. I don't know how those systems work.

I was agreeing with your statement by providing a piston analog

The very article you linked to to says:
The system uses power from the engines, thus reducing their maximum performance. With the anti-ice system on, the highest altitude at which the overloaded aircraft could fly – without stalling – was reduced to 31,900 feet (9,700 m).

That was ratchet freak not me.

In addition to robbing power from the engines, it also increases fuel consumption and there are often temperature related limits to which prevent overheating of the surfaces being deiced.  For instance, in my jet, anti-ice is not permitted to be on when the outside air temperature is +10C or higher.

@Lnafziger, it's not as much in addition to as as a result of reducing thrust. You either fly slower at the same flow rate or increase the thrust setting, and thus flow rate, to maintain speed and either way you burn more fuel for the trip. (It is certainly important aspect; thanks for mentioning it)

How about "as a result of decreased thrust" then, lol.  I see you incorporated my first point into your answer, but the second point is also important to mention, in my opinion.

It depends on the type of de-icing system.
A jet like the MD-82 on that flight will use bleed air from the engines which supplies TAI (thermal anti ice) for engine nacelles and wings. That extra bleed air taken from the engines lowers their power output and decreases the fuel economy. If you are limited by EGT for available power, turning on anti-ice is going to degrade your climb performance.
Likewise, on a descend using anti-ice might require running the engines higher than flight idle to supply enough air, which effects the descend path and lowers fuel economy.
So, on a jet with thermal anti-ice, it's not exactly dangerous to run the anti-ice when it's not needed, it just lowers your performance and economy a bit. If you on the other hand need every little bit of power you can get (following an engine failure for example) turning off anti-ice might give you just that bit of power.
On certain, mostly propeller powered aircraft, however there's a different system for de-icing (note that it's de-ice, not anti-ice) that works with inflatable boots on the leading edge of the wings and/or horizontal stabilizer.
The idea is that you let a sheet of ice accumulate on the de-icing boots, and then inflate them using a compressor, which breaks the sheet of ice that is then blown away. Turing on the de-icer will normally cycle the compressor so it inflates and deflates the boots in regular intervals to break off accumulating ice. Turning on those de-icing boots too early will accomplish nothing, because the boots can only break off sufficiently hard ice. Some manuals even consider turning on the boots too early (less then 1/4" of ice accumulation) harmful, as the ice might not be hard enough to break off cleanly and instead stick to the boot. This advise is found in some older manuals, I do not have any hard evidence if this is still considered best practice or if it is an old wive's tale.

It looks as if you didn't finish your answer. What effect does the boot system have on performance or other flight characteristics?


text:
Why, and how, are barometric altimeters accurate enough for approach and landing?
The barometric altimeter is used as the primary altitude indicator during approach and landing right up until the aircraft crosses the threshold (after which the radar altimeter takes over and makes the “thirty...twenty...ten” calls), as it - unlike the radar altimeter - can’t be fooled by mountains or canyons lying across the descent path.
Yet barometric altimeters have problems of their own:

They require an accurate knowledge of the local surface pressure at all times... and atmospheric pressure can change very rapidly, both from time to time and from place to place.
They require that the aircraft be at a specific, constant angle of attack in order to give accurate readings; if the aircraft is flying at a higher angle than that for which the pitot-static system is calibrated, ram air will be forced into the static ports, resulting in a falsely low altimeter reading.
They rely on the aircraft’s static ports, which can be blocked by things such as rain, icing, or duct tape (fortunately, this is uncommon nowadays, as most static ports are heated, and most maintenance techs quadruple-check that they haven’t left anything covering the ports).

Given these vagaries of barometric altimeters, why don’t we see lots of crashes from situations like these:

You break out of the clouds at what your altimeter says is 3000 feet; unfortunately for you, it turns out the pressure’s dropped since the airport’s altimeter setting was last broadcast, and you’re about to hit the ground (either this or the following could, in the wrong circumstances, be exacerbated by torrential rain, which commonly occurs in conjunction with low-pressure systems, and can potentially be ingested by insufficiently-heated static ports, resulting in an even-more-falsely-high altimeter reading).
While on approach, you enter a localised low-pressure cell that the airport’s AWOS, being at the airport rather than back along the approach path, doesn’t know about.  Seeing your altitude apparently ballooning up, you idle the throttles and push the nose over to correct the altitude excursion; unfortunately, since you were never actually too high in the first place, this action instead sends you below the glidepath, and straight into the ground.
During a go-around, you set TOGA power on the throttles and pull back on the yoke; as the elevators are quicker to respond than the engines, the aircraft pitches up before it can accelerate much, resulting in the aircraft’s angle of attack temporarily increasing.  Ram air enters the static ports, the altimeter says you’re lower than you actually are, and, in an attempt to avoid hitting the ground, you pull the yoke as far back as it’ll go, stalling the aircraft.

When have you ever experienced, sitting on the ground, the air pressure changing the equivalent of 3000 ft in a matter of minutes? Or even days? It seems you have created a bunch of very implausible scenarios (somebody designed a static port that looks like a pitot probe) and are asking people to discount them.

@user71659 Indeed -- 3000ft is about a 10% change in pressure, which is a huge amount of variation unless there's a hurricane passing by.

Yes, but while you're approaching a runway without visibility with cloud bottom very close to the ground (your scenario), you are likely using an ILS to set the aircraft altitude, and using a radio altimeter to track the distance to the ground (with aural annunciations like "One thousand!"). So it should be easy to detect a problem with the barometric altimeter and abort the approach.

A difference of 1 hPa results in an error of 27ft in the altimeter. To have the altimeter showing 3000ft when the aircraft is actually at sea level, the altimeter must be off by 111hPa. Standard air-pressure at sea level is 1013 hPa (that's converted to 29.92 inHg for you Americans).
For comparison, the pressure in Hurricane Katrina reached as low as 902 hPa. So if you were flying into a hurricane but left the altimeter setting at 1013 (which is used as the standard setting at cruising altitude), you could theoretically pop out of clouds at what you thought was 3000ft but instead hit the ground.
Ignoring the fact that nobody tries to land in a hurricane, this mistake is prevented by the airfield pressure being reported by ATC, in the ATIS, and even an alert from the aircraft if it is advanced enough.

While on approach, you enter a localised low-pressure cell that the airport’s AWOS, being at the airport rather than back along the approach path, doesn’t know about. Seeing your altitude apparently ballooning up, you idle the throttles and push the nose over to correct the altitude excursion; unfortunately, since you were never actually too high in the first place, this action instead sends you below the glidepath, and straight into the ground.

Pockets of low pressure as you describe just don't exist to that degree. Hurricanes take hundreds of kilometres to reach their low point. And anyway, this is why airliners have a requirement for the approach to be stabilized at a specific point -  typically 1000ft above the aerodrome level. Any significant deviation from the glideslope below this point mandates a go-around.

During a go-around, you set TOGA power on the throttles and pull back on the yoke; as the elevators are quicker to respond than the engines, the aircraft pitches up before it can accelerate much, resulting in the aircraft’s angle of attack temporarily increasing. Ram air enters the static ports, the altimeter says you’re lower than you actually are, and, in an attempt to avoid hitting the ground, you pull the yoke as far back as it’ll go, stalling the aircraft.

Altimeters are calibrated with multiple static ports and designed so AoA changes do not noticeably affect the altimeter. For the rest of this example, I mean I suppose a pilot could just forget the basics of flying but it's unlikely. Pilots know how to select the correct pitch and power to guarantee maximum climbing performance.
You didn't mention that altimeters are also affected by temperature, and in cold air they will read higher than reality.  There is no correction for this, and so some approaches will have limitations in very cold weather. EDIT: See John K's comment below.

Last paragraph is incorrect.  There are standard temperature correction tables for IFR approaches that you use when it's below freezing to correct for altitude temperature error on altitudes such as MDAs, DAs, and step down levels within the approach.  Radar vectoring altitudes are corrected for temperature by ATC.

See this article http://twinandturbine.com/article/how-low-did-you-go/

@JohnK I was meaning there is no correction within the altimeter itself like there is for pressure. But you're right, thank you.

The OP is talking about effect of AoA on the pitot, dynamic air pressure. Which is not part of the static air system. Also for the Americans 0.01"Hg =10 feet altitude.

Pressure rise at the static ports, caused by crosswinds or sideslip, is compensated by having a second static port on the opposite side of the aircraft.
The traditional static system simply connects both in a T junction, modern types use two separate static pressure sensors and combine the data in the ADC to avoid leaky plumbing.
This design also adds redundancy in the event of one side being plugged.

Baro altimeters are generally required to be accurate to +- 50ft when set to local altimeter setting, and the lowest you can descend on baro altitude (a Cat 1 ILS with a decision altitude) is 200 ft, so there is ample margin in the most critical case (to descend any lower on an approach, that is, Cat 2 or 3, which has a decision height, not altitude, you need a radar altimeter).
The actual altitude sensitivity of a typical baro altimeter is less than 10ft. That is, the needle will move to show that much change, especially when there is some vibration source present to overcome bearing "stiction" in the mechanism (On gliders without any vibration present, they are a bit less sensitive and tend to stick a bit until the pressure change is enough to overcome bearing friction, and they may not indicate a change until 20 or 30 feet unless you tap on the panel if the unit has aged a bit).

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
How does a diffuser (in ground effect) accelerate the air in front of it?
A diffuser reduces speed and increases pressure, so how does a diffuser accelerate air in front of it if we have an adverse pressure gradient situation?
Wouldn't be better that we put the lower pressure (instead of higher) on end which will "pull"/accelerate air in front of it?
Example of F1 diffuser in ground effect:

Where is the diffusor? The question is unclear.

@PeterKämpf, at rear  floor on F1 car,https://www.youtube.com/watch?v=FMojq8Qj5MY..

@PeterKämpf,is it possible that nobody at physics site and aviation site dont know answer?

Would this question and its answers help?

Even though this isn’t strictly an aviation question, it does involve aerodynamic principles.
To put it simply, the diffuser’s main purpose is to gradualize the transition from rapidly flowing air under the car’s body as it transitions back to the speed of the ambient air behind the car.
There is a high pressure zone in front of the car from air particles colliding with the vehicle, and a low pressure zone in the wake behind the car as airflow is attempting to rejoin on the other side. This high to low flow draws air under the car where space is limited. This limited space results in an increase in speed and a decrease pressure, thus increasing downforce as the pressure below the car is less than the pressure on the top and sides of the car. This is Bernoulli’s equation at work.
However, the rapidly moving air experiences adverse pressure gradient at the rear of the car and airflow separation results in significant turbulence. This turbulence not only increases drag, but limits how quickly air can be evacuated from underneath the car. By carefully shaping a diffuser, the airflow can be slowed more gradually, easing its transition back into the ambient flow, minimizing turbulence which increases the flow speed under the car, decreasing the pressure and increasing downforce on the wheels even further.
The diffuser is shaped to increase the airflow speed in front of this funnel to ‘push’ a low pressure zone in front of the funnel, more effectively drawing air into the diffuser.

,,,wouldn be better to put wing low pressure side on the end of floor,so low pressure from wing will "suck/accelarate air  under floor,so in this case we dont have adverse pressure gradient-situation?

The low pressure side IS under the car, where the strakes begin and air is accelerated into the front of the diffuser. The diagram you have up there isn’t precise to scale, it just shows the general region that the adverse pressure gradient begins. It can’t be avoided altogether. The airflow is going to separate from the underside surface. It’s just a matter of making that transition as smooth as possible. There are wind tunnel videos you can look up that use smoke to show the difference in turbulence with and without a diffuser.

is pressure in diffuser lower than atmosferic pressure?

Pressure in a diffuser is in transition from much-lower-than-ambient-atmospheric-pressure to a pressure that matches the low-pressure zone in the wake of the car, which is still lower than ambient, but higher than the flow underneath the vehicle.

,So diffuser itself produce significiant downforce because his average pressure is lower than ambient pressure?

The diffuser allows the pressure under the entire car to be lower by increasing the efficient evacuation of airflow. Put simply: the air particles passing through the diffuser do a better job of getting out of the way so that they don't bunch up and slow down the particles coming behind them. This makes air flow faster under the entire car, decreasing pressure, which increases the downforce on the entire car, not just at the diffuser itself.

@NoahPrandtl: On the aerodynamic coefficient chart in your link, the 2019/20 models produced -2.06 out of a total -3.75, or 54.9% of total downforce. The 2021 derived less total downforce from the floor, -1.69 out of -3.36, but this low pressure was more evenly distributed across the bottom of the car due to a reshaping of the diffuser. As you can see, the ‘21 diffuser causes a more gradual release of pressure than in previous years. Aggressive strake funneling on the ‘19/‘20 dramatically decreases the pressure at the opening of the diffuser, localizing downforce in the vicinity of the axle.

@NoahPrandtl: Not at all. Each diffuser can be shaped to create the desired aerodynamic effects within a certain range of variance. In the image of the ‘21 car, you can see the diffuser working in the way I described - facilitating a more uninterrupted flow of air from the front of the car to the back. In the ‘19 and ‘20 car images, you can see the rounded pressure gradient being ‘pushed’ in front of the diffuser Venturi area since airflow is being tightly restricted and accelerated again just in front of the rear axle. This localizes downforce at the axle.

Here is a good video explanation. https://airshaper.com/videos/what-is-a-car-diffuser/video/9UgacwMJpuk

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is the 737-800 a different plane from the 737 MAX 8?
I am flying on March 16 from Barbados to Toronto on a Westjet Boeing 737-800 also referred to as an aircraft type 73H on my ticket. Is this a different plane from the Boeing 737 MAX 8, grounded by several countries?


text:
Why do airports remove/realign runways?
When looking at Google Earth, I often find myself looking for airports. I often notice that no matter what size airport, over time many of them have abandoned old runways and built new runways in different directions.
It doesn't matter between rural and urban, so residential doesn't seem to be the cause. Is it that the wind direction changed from decades ago? Did they decide that sunlight matters more or less at some point in time? Anything to do with Earth's magnetic field?

In some cases the prevailing winds change and certain runways fall out of use. Since airports tend to be land limited they may wish to use the land for hangars or other facilities so the runways are eventually decommissioned.
In other cases it could a noise abatement issue, many airports predate the property development that often surrounds them. It may be in the best interest of the local neighborhood to change the runway orientation to one that creates less noise and pollution over homes or businesses.
In some cases runways may be moved to comply with changing regulations as was the case at Aniak Airport, where an existing runway no longer complied with obstacle clearance regulations.
In some cases it also becomes expensive to maintain a runway that may not see much use and it will be shut down.

Magnetic shift generally wont cause a runway move but it may cause a runway re-number since the runways are numbered as per their magnetic heading.

thank you for your reply.  I did look up Aniak and found a youtube video of the local Alaska legislatures shaking their heads at having to spend an estimated $53M to move the runway.

@doug literally shaking their heads?

Three runways (or pairs) 60 degrees apart was very common. Where land was limited, two runways (or two pairs) at 90 degrees was almost as good. These generic designs could be built very quickly almost anywhere and work well regardless of the prevailing winds, which was particularly important when building hundreds of them in a hurry during WWII.
However, the needs are different. Modern jets need longer runways than WWII planes but aren't as sensitive to crosswinds. And there is now decades of data on which runways were used the most at each airport, so only those were extended.
At the same time, traffic has grown, and building new runways parallel to the main one(s) adds capacity faster than it adds costs, so it makes sense.
Some airports kept the intersecting runway(s), but it(they) don't provide anywhere near the capacity now, still cost a lot to maintain and take up valuable land that could be reused for fancy new terminals or hangars, so many airports have ripped some or all of them out.

Thank you for your reply.  Your answer has helped my understanding, especially regarding the idea of how quickly so many runways must have been built across the country.

One example where you can see that change from 60-degree-separated runways to longer parallel runways is Heathrow. Even in current aerial photos, the location of the old runways is still clearly visible. The two 09/27 runways were extended, the other runways were turned into taxiways, ramps, and built over with terminals and other buildings.

+1 for mentioning adding parallel runways. This seems to be the primary reason for large commercial airports. As the required capacity keeps growing, several commercial airports have gone away from having crosswind runways at all in favor just having as many parallel runways as they can, which is by far the most efficient if it's feasible. ATL comes to mind. ORD is another example  where old runways in different directions were closed or turned into taxiways to make room for more parallel runways.

Just to note, the part about runways being built in WW2 would be specific to mainly European countries, no?

@Michael You can see it across the US (training bases) and Pacific islands (operational bases), not just Europe, and I'd assume anywhere the air war reached. The same designs appear postwar in other countries too, just not as many of them.

In the US, one of the most common reasons to abandon one or more runways is that a large military airbase built for intensive World War 2-era training has passed into civilian hands-- county, municipal, or private ownership-- and it is too expensive to maintain all the runways, especially considering the vast reduction in traffic.  For example, if you visit the airnav page for SN76 and look at the aerial photo, you'll see the short stretch of fresh blacktop on the one maintained runway, with remnants of a vast system of other runways and taxiways still clearly visible.  This former military airfield is now privately owned.
This explanation wouldn't apply to small airports though-- there would at least be some visible evidence that a larger airport had once been there!

Thank you for your comment.  I do often find myself looking for small civilian airports and find myself wondering about their history, and why the change.  For instance, I found the Canyonlands airport outside Moab, Utah.  Nothing that I could see that would necessitate a change, yet there it was clear as day.  I completely understand your comment regarding WW2 runways as we have several abandoned airstrips in north Florida.

@doug Yeah, the area around Eglin AFB has tons of those abandoned and/or repurposed runways. It's pretty interesting to look around there on aerial imagery. Old runways turned into parking lots for rusted-out tanks and such.

Some airports have had to rebuild runways as the size and weight of planes using them has increased.   Occasionally, the underground geology under the old runway may not be suitable to support the newer heavier planes.  For example, a runway built near the water may be on soft or marshy ground.  This ground may need to be reinforced to handle heavier planes.
Also, it is generally not desirable to take a runway out of service completely while rebuilding it so you will build a new runway nearby and then decommission the old when one when the new one is complete.

It is not about a change in winds, but more about having any weather data at all. Recording weather was very primitive even 60 years ago. and many locations cicra world war 2 did not have any recorded wind data beyond a local farmer holding up a finger giving a generalized guess. so they did the 60 or 90degree thing. Many WW2 airports had a triangle of three runways, one will get very little air-side use and may be used mainly for taxi.
Another change is in the instrument approach procedures. These, like weather information, were also very primitive in the 1940s and it may be difficult to make a modern procedure to certain runways due to terrain obstacles or competing airspace issues. In these cases a runway may have less value than its cost to maintain. Also you don't want a VFR plane using a crossing runway in marginal visibility while an IFR flight is on final approach when the tower is closed.

It's not just (lack of) weather data, particularly for repurposed WWII-era military airports.  It's that the planes were mainly fairly high-performance taildraggers, which didn't handle crosswinds all that well.  So even if 90% of the time winds favor one runway, if the other 10% you have a strong crosswind on it, you still want to be able to take off and land.

"IFR flight on final approach when the tower is closed"? IANAP, but can you fly IFR into an untowered airport with declaring an emergency?

@FreeMan Yes, IFR to untowered airports is normal everyday procedure. Both for private and air-carrier operations.

#TIL. As I said, not a pilot...

Multiple reasons.
1) Changes in prevailing local winds can necessitate new runways though this is probably the least desirable reason to do this as runways cost between \$1-\$3 million per mile, depending on type, layout capacity, etc.
2) Airport expansion and upgrades to accommodate larger heavier traffic.  Sometimes this is possible to simply upgrade or lengthen an existing runway.  Often times preliminary civil engineering studies conclude this is not practical and a site for a brand new runway is chosen.  One prime example of this was Van Nuys airport (KVNY).


text:
Would random sitting arrangement be the best way of boarding for passengers?
This is more in relation to flights which have a single class of passengers with a short haul flight duration. Why don't airlines adopt random seating arrangement i.e. first come first serve basis. We already see business class passengers of having the flexibility of boarding at their own convenience.
This might solve the problem of boarding, and might also encourage people to board quickly.
To solve the issue of cabin baggage, we could have dedicated space for each passenger, by dividing the existing baggage space by the number of seats below. This would take care of 'greedy' passengers. Also, passengers can check beforehand if they are carrying excess luggage.

This would solve the problem of boarding, and would also encourage people to board quickly - what evidence do you have to support this claim?  I can see it bringing out the worst in some people and a chaotic, inefficient "free for all".

I can't answer why won't airliners allow for random sitting arrangement, but I can tell you that the method of random sitting arrangement would be a faster way for filling up the cabin, but it is not the fastest technique. I use the information from a Nova episode (S41E03) called, Making Stuff Faster.

@Simon: Edited the question, apologies for my poor grammar

UK's big low cost airline used to do this, but reverted to allocated seating a couple of years ago. I can tell you that far from being efficient, it was the expected free-for-all, and therefore was a nightmare. You try battling through 100 people desperate for their favourite seat when you have 2 small kids and a pushchair to get boarded. Not fun at all.

The Mythbusters tested various boarding patterns in their previous season (see the digest here, full episode here) and came to the conclusion that "random-random" (close to Southwest-style) was the fastest way to board (though the least liked), and that the current most common method among traditional airlines (back to front) was the slowest. Alternate styles including two forms of "WILMA" boarding (Window-Middle-Aisle, United does this) and "Reverse Pyramid" style (which U.S. Airways used to use) were both fast and very well-liked by the volunteers. I have some issues with their testing methods though:

They only allowed for a single test of each boarding plan, using the same group of volunteers each time. That means two things:

Order of testing matters, because your group will generally become accustomed to getting on and off a plane, which will speed things up as the day progresses.
Any "noise" inherent in a variable of the test that you are neither controlling nor testing cannot be cancelled out and can skew the results.

They tested the control (back to front) first, meaning their volunteers were totally unfamiliar with the "plane" and thus would be expected to be slowed by inefficiencies born of this unfamiliarity. If no other test were repeated, it should have been this one (at the beginning and end of the day) to compensate for this.
First/business class were always boarded first (this is common but not universal among airlines), while every other ticketed passenger regardless of age was boarded according to their individual seat, with only "lap children" boarding with their parent (airlines nowadays require a ticket and seat for anyone over 2yo, so boarding families with pre-adolescents was not really tested). This is opposed to other variables such as overloaded passengers, guys heading "upstream" to the lavatory etc which they sprinkled in to spice up each boarding experience.

One final thing; boarding faster only means you're sitting in a cramped airliner seat longer. Getting passengers aboard an airplane is usually the easiest and quickest part of turning an airliner around. Unloading/loading baggage, refueling, preflight checks etc all take longer in the aggregate than anything going on inside the cabin.

I have now seen the video and think that the experiment should have been carried out at an actual airport

Unless I misunderstand you, many airlines already do this. You buy a ticket, you join a queue and you sit in the first available seat that is acceptable to you.
I find it leads to fitter younger people sprinting to the front and leaving the old and frail with the worst seats. Some airlines prioritize boarding for adults accompanying children and a few other categories.
As ManuH commented. Unallocated seating often leads to families being separated inside the cabin and sometimes to prolonged multi-way pre-take-off negotiations with other passengers to try to arrange swaps to get a seat in the same general region of the plane as your loved ones.
Personally I find a preallocated seat number and boarding prioritised by row number leads to a  more civilised experience and fewer scrums arise in the aisles as prior passengers try to stuff luggage into overhead lockers above seats near the doors.
There are many ways of defining "best", speed of boarding is only one of them. This is perhaps why no airline yet bales up their passengers and loads them by forklift.
I recall the USAF has seats attached to freight pallets that it uses for troop transport, maybe the future of aviation is to be strapped into your seat in the departure lounge and be mechanically loaded from one end of the fuselage?

This is done on European low cost carrier, and leads to passengers traveling together to be spread along the aircraft as first boarded takes seat next to an empty seat, resulting in remaining empty seats isolated

"I find it leads to fitter younger people sprinting to the front and leaving the old and frail with the worst seats" - The first couple of rows could be blocked for old and children

@Firee: How many rows would you block off for middle aged people with a stiff knee? In practice, the sort of airlines that use free-for-all seating, in my experience (first encountered this in Oahu - relatively OK and later in Belfast - not so OK) did not rope off seats, they just give the slower pax a head start before unleashing the frustrated frenzied trampling rabble at them.

Regarding the last paragraph, we've got you covered.

Does the Air Force board the pallets before they're loaded? I was under the impression palletized seating was just a way to secure seats to a plane designed for generic cargo.

The pallet idea seems cool...

@cpast - That was my understanding as well; this system is basically the USAF's version of a "combi" airliner, able to be reconfigured for a variable mix of cargo and people. Strap seats to the same roller pallets used to load vehicles, food or ammo, lock them to the deck, and voila, troop carrier.

My last paragraph was written tongue in cheek.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Instrumented landing: why switching *everything* off
Few days ago I took a flight to go back to my town. Towards the end of the journey, the captain demanded us to shut down any electronic device that we had on board, including iPods, CD players, phones and so on. Reason: there was very low visibility and we had to start the instrumented landing.
From what I could understand, an instrumented landing system allows and aircraft to be centred on the lane assisted by signals delivered by an ILS (a localiser and a glide slope), so to arrange the maneuver without visibility. This signals are in the  110 MHz (LOC) and 330 MHz (GS) frequency range.
Given that for the take off, "manual" landing and the journey itself, shutting off the devices is not required any longer (and there are signals travelling even there I would guess, at least for what concern communication with the base and all the ariplane intra-components communications), why is that instead required for an assisted landing? What interferences could a CD Player possibly produce on the instrumentation to an extent that it's more dangerous than with the usual take off - flying - landing phases?
On a side note: as you probably understood, my level of expertise is very low, so forgive any dumb mistake or oversight.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why can't the 737 MAX's horizontal stabilizer autotrim be cut out by control yoke inputs?
According to this article, a horizontal stabilizer runaway on the 737 MAX, unlike with all other 737s, cannot be countered with yoke inputs:

Older 737s had another way of addressing certain problems with the stabilizers: Pulling back on the yoke, or control column, one of which sits immediately in front of both the captain and the first officer, would cut off electronic control of the stabilizers, allowing the pilots to control them manually.
That feature was disabled on the Max when M.C.A.S. was activated — another change that pilots were unlikely to have been aware of. After the crash, Boeing told airlines that when M.C.A.S. is activated, as it appeared to have been on the Lion Air flight, pulling back on the control column will not stop so-called stabilizer runaway.

Why would the addition of MCAS require removing the yoke trim override mechanism?  In the event of a trim runaway, the pilots' first reaction is going to be to pull (or push, depending on the direction of the runaway) the yoke, and requiring them to perform a separate, different action in the heat of the moment to disable the autotrim mechanism is an unrealistic expectation; allowing yoke inputs to cut out the autotrim relieves the pilots of the burden of having to recognise the problem as a trim runaway in order to solve it, and allows the problem to be solved in the same manner as other unwanted pitch excursions (by pushing and/or pulling on the yoke(s)).

Allow me to emphasize the article quote differently:

That feature was disabled on the Max when M.C.A.S. was activated

For a regular trim runaway without MCAS activation, the yoke can still cut out electronic trim as before. The only change was inhibiting this behavior when MCAS is active. MCAS is designed to improve handling at high angles of attack. One way to get to a high angle of attack is with lot of yoke input, so it would somewhat defeat the purpose to stop MCAS in that situation.
The designers chose to trust MCAS (and its sensor inputs) over the pilot inputs in this situation. It certainly seems now that this trust was misplaced, but this has more to do with the system design than the general philosophy. Fly-by-wire planes have many protections that will change control input depending on sensor inputs. In normal law, Airbus alpha protection will prevent the angle of attack from increasing, even with full aft sidestick input. It compares three sensor inputs to do this, rather than trusting only one, but even that is not infallible.

You have to consider why MCAS was installed. It's there to save the day when the pilots have not kept the angle of attack to appropriate levels, very commonly due to disorientation.
If MCAS could be overridden just from the pilot pulling back on the yoke, it defeats the purpose of it being there in the first place. Hence, when MCAS is active, the autotrim must be cut out via a different method.

I disagree: MCAS was installed to help pilots lower the nose when they are close to a stall in a high thrust situation, where pushing on the yoke alone might not be enough. The purpose was never to overwrite a pilot's input and it really shouldn't be active when the pilots are pulling against it (and likely it won't after the update, which is about to be released in the next months).

@Bianfable: According to Boeing, post-update, MCAS still won't automatically disengage if the yoke is pulled, but its control authority will be limited to inputs small enough to counter with elevator deflection alone.

@Sean That's interesting. I expected they would add this additional cut out feature. Maybe the changes they mentioned are enough to never be an issue any more. Anyway, my original point remains: MCAS should not fight the pilots, it was designed to make the MAX feel like the NG to fly in high thrust and high angle of attack situations.

@Bianfable You are right, but Boeing want it transparent to the pilot, expecting that a single step  of THS 2.5 ° would be sufficient, if the yoke was able to cut this, the runaway would have been declared like a fault by the pilots.


text:
Why does the A320’s maximum allowable aileron deflection decrease, rather than increase, when the flaps are extended?
According to this answer to why the A320 uses mainly spoilerons for roll control during landing, rather than conventional ailerons, the ailerons can’t extend as far when the flaps are extended, for fear of stalling the wing:

Downward aileron travel must be restricted when flaps are deflected. Since flaps change the local incidence on the flapped part of the wing, the outer wing will experience an increase in its local angle of attack. The increased suction over the inner wing will accelerate not only the air flowing over the inner wing, but also that air which will flow over the outer wing as well. Left to itself, the outer wing would stall if powerful Fowler flaps are deployed on the inner wing.
Adding slats will push the stall angle of attack up, and now the outer wing is back in business. However, if the aileron is deflected downwards, the stall angle of attack is reduced again. The outer wing could stall simply due to the aileron deflection!

Which would make sense - after all, if the trailing edge of the wing is already angled more down than usual, then it can’t safely extend as far further down for roll control than it would be able to do otherwise - if not for the fact that the ailerons aren’t located on the portion of the wing with the flaps on it (they’re located near the wingtip, where they’ll be more effective at rolling the aircraft, whereas the flaps are located near the wing roots, where there’s more space to store them and they won’t increase the bending stresses on the wing as much), and, since extending the flaps increases the amount of lift produced by the wings at a given speed and vertical load factor, thereby allowing the aircraft as a whole to fly at a lower angle of attack than it would be able to do with the flaps retracted, the A320’s allowable aileron deflection should increase when the flaps are extended, since the lower attack angle of the unflapped, aileron-containing portion of the wing should allow the ailerons to deflect further without stalling.  Indeed, the A320’s direct competitor, the 737, exhibits precisely this behaviour, where higher flap settings increase the allowable aileron deflection (and, thus, the lateral control authority available) for a given indicated airspeed and vertical load factor1 - so why does the A320 behave in precisely the opposite way?

1: This means, for instance, that the 737’s crossover airspeed, like that of essentially all aircraft, decreases as the flaps are lowered, whereas, if the aforementioned quote were accurate, the A320’s crossover airspeed would increase at higher flap settings!

Where's the reference for the 737 behaving in the opposite way? Is it somewhere in the references in the linked question?

@fooot: Not only that, it's in the portion of the references that is specifically quoted in the question itself.

I'm not seeing where you're getting allowable aileron deflection from that table. It looks to me like it's just listing the control wheel input needed for the different conditions.

@fooot: ...which is an indirect measure of aileron effectiveness, and, therefore, the available aileron authority.

Would this answer be sufficient or do you need more information?

@PeterKämpf: The latter.

Effectiveness changes with airspeed and aircraft configuration so it can't be assumed to only be a result of authority. The 737 is also not fly-by-wire so changing authority based on flap position would be more complex.

You may add drawing of the aileron and flaps to clarify your description.

You assume that

the lower attack angle of the unflapped, aileron-containing portion of the wing should allow the ailerons to deflect further without stalling.

but that only looks at the geometric angle of attack. What counts, however, is the induced angle of attack. Since the flaps on the inner wing create much more lift, the induced angle of attack is much higher than for the clean configuration at the same geometric angle of attack. Consequently, the outer wing will stall at a much lower geometric angle of attack, and adding trailing-edge-down aileron deflection will stall the outer wing with only a medium angle.
Add to this that the spoilers are much more effective for creating rolling moments once the flaps are deployed and will avoid the adverse yaw of an aileron deflection due to their high drag on the down-going wing, and the spoilers are a much safer option for roll control that the ailerons are in landing configuration.


text:
What are the regulations for crossing the Atlantic in a twin engine prop plane
Are there ETOPS like regulations for private planes?
If the plane has the range (4000km+), can it do it in one go?

A prop plane would have a couple of choices.  The northern route: Canada, Greenland, Iceland, then England or Norway. Or the southern route: eastern coast of Brazil to west coast of Africa, like Sierrra Leone.   Lot of overwater time either way.

You say twin engine prop plane, then say private planes. Which one are you asking about? There's a big difference between an ATR72 and a DA42, both of which are considered twin props.

It's quite common to fly single-engine prop planes across the Atlantic.  E.g.. https://www.aopa.org/travel/international-travel/transatlantic

Aircraft operating under Part 91 have no ETOPS requirements. ETOPS is only applicable to Part 121 and Part 135 operations. FAR 121.161 only applies to operators of twin-engine turbine aircraft in scheduled airline service. The rules for Part 135 are in 14 CFR Appendix G to Part 135, Extended Operations (ETOPS) and excludes multiengine transport-category turbine-powered aircraft.


text:
Why are "Follow Me" cars painted yellow and black?
Why are "Follow Me" cars painted black and yellow, and use square shapes in their design?

So that they are easy to see.

Not all follow me cars are painted yellow and black.

Ever notice how the lines on the airport are painted yellow on (mostly) black asphalt? You follow the yellow lines on taxiways and to get off the runway at a taxiway. So it might make sense to have the same color scheme. I’ve only seen golf carts as follow me vehicles, and never painted yellow, so I’m guessing it’s not a standard of any sort.

White/black has the highest contrast, which is why most countries use only white paint on roads.  US/CA use yellow to divide opposing directions due to the extra danger (see answer below) even though it's slightly lower contrast; some countries use yellow instead of white on roads frequently dusted with snow for all-season contrast.
Applying these conventions for runways and taxiways is fairly obvious, especially when you consider that airports will spend more effort keeping runways clear of snow than taxiways.

Yellow and black together are highly visible in any light, especially if there are sharp, straight lines between them; our eyes are drawn to that combo and our brains are evolved to recognize it as a danger. Think of bumblebees.
Stationary objects tend to be painted white and red for similar reasons.

It is because when you are taxiing behind the follow me in a dark night with a dark pavement it will make the car become more easy visible to the pilots, specially in low visibility operations

Welcome to the site! What you say seems to be true but it just duplicates what the existing answer says. We're really grateful that you're trying to help but please only answer if you have something new to say.


text:
What are these two fins on the JF-17 used for?

What is the name of this fin?
What are these two fins used for?

What aircraft is this?

@MichaelHall, JF-17

Where did you get the picture from? It's considered polite to indicate your image sources (actually, it's required for copyright reasons).

@FreeMan, I lost the source. Sorry for that!

That's why it's appropriate to include it when you ask. ;)

They are called ventral fins and can be seen as a downward extension of the vertical stabiliser(s). And like any vertical stabiliser(s), their main goal is to provide yaw stability.
They can normally be found on fighters, mainly for the following reasons:

if the aircraft is embarked on aircraft carriers, the low height of storage decks and elevators limits the height a vertical stabiliser can have. That's also why many embarked fighters have two short main vertical stabilisers instead of one single big one.

at high AoA, the wing can aerodynamically shadow the main vertical stabiliser(s) while the ventral fins remain effective.

in respect to the main vertical stabiliser(s), vertical fins have a "squatter" shape (i.e. lower aspect ratio) which if on one hand gives a lower $C_{l_{max}}$, on the other hand gives also a smoother stall and at an higher AoA (and that's why, in general, tailplanes have a small aspect ratio).

Fins don't have to be confused with strakes:

Strakes resemble fins but they are normally smaller and added after the first flight in order to "correct" small aerodynamic issues which couldn't be foreseen at design phase. In this particular case (red circle on the F-18), they have been added to divert turbolent airflow detaching from the leading edge at high AoA: without strakes this turbolent airflow impinged on the vertical stabiliser generating vibrations.

BTW, I promise I'm not being petty, as I appreciate you pointing out my mistaken use of "longitudinal"...  But after re-reading your answer, you are similarly mistaking lateral stability for vertical stability.  Vertical tail strakes that reduce rudder/vertical stabilizer height would provide vertical stability (which by by definition is yaw stability about the vertical axis), not lateral stability (which is by definition pitch stability about the lateral axis.)  And the ventral stability fins on many aircraft are formally called strakes, not just the small "airflow correctors."

@Max: don't worry, I'm not Einstein nor Kelly Johnson :)  With longitudinal I mean pitch and with vertical I mean yaw. But I understand that they might be mistaken and I'm going to correct my answer according to your comment. Formally I don't know, but technically strakes are small surface's added after the first flight in order to correct small aerodynamic issues which couldn't be foreseen at design phase. On the other hand, fins are stabilising surfaces which have been there since the aircraft was still only a model on a computer (or on paper)

@Max: corrected, thanks for your comment  Btw roll stability is lateral ;)

Your Einstein/Johnson answer is the EVER.  But, your comment is not correct, LOL!  The Lateral Axis runs wingtip to wingtip.  The vertical axis is vertical through the plane's CG.  The longitudinal axis is tip to tail.  Stability is referenced to moments about an axis.  By definition lateral stability is pitch stability about the lateral axis.  By definition, vertical stability is yaw stability about the vertical axis.  By definition, longitudinal stability is roll stability about the longitudinal axis.  Illustration: https://pilotinstitute.com/airplane-stability/

I think I messed things big time :) That's why in my updated answer any reference to lateral/vertical/longitudinal is now gone

We are neither Einstein nor Kelly Johnson.  ;)

They’re often called ventral strakes, or simply ventral fins.  In some high performance fighter aircraft, the Center of Pressure (CP) is located very close to, or even behind the Center of Gravity (CG), to intentionally create a very small, or sometimes even negative pitch stability.  This CP placement allows for a lot of very aggressive pitch maneuverability, often coupled with very large elevators, and often stabilators.  However, this CP placement also introduces a couple of challenges.

It can introduce some undesired nose-down moments in some flight attitudes or maneuvers.  This is especially true if the wing is shielding the horizontal tail, which is exacerbated by large stores on wing pylons.

It makes the aircraft less stable around it’s vertical (yaw) axis as well.  Yaw can be introduced by the asymmetric drag as weapons on either side of the airplane are fired from their wing stores, as well as adverse yaw from large aileron deflections during brisk maneuvering.

Designing in more vertical axis (yaw) stability can involve undesired trade offs…  Moving weight forward, a taller vertical tail and larger rudder, or procedural constraints to weapons deployment symmetry.
Another approach is to use strakes.

Vertical strakes such as those shown move the vertical axis CP (center of pressure) further back on the aircraft.  They also increase spin resistance when the vertical tail is shielded in high-AOA, high-G maneuvers.

Angled strakes (think F16 but also many business jets) create both vertical (yaw) stability and lateral (pitch) stability.

Usually when you see strakes it means that wind tunnel testing revealed some undesirable yaw or pitch characteristics in certain configurations or maneuvers that the designers needed to damp out.

I think you are confusing lateral stability with longitudinal stability. Ventral fins improve lateral stability, not longitudinal. Plus, strakes are something totally different than the vertical fins in the picture. So except the very first line, the rest of the answer should be updated.

I changed my answer for clarity, thanks Sophit.  Strakes are not definitionally lateral axis devices, a vertical fin as shown would also be called a strake even though positioned differently than on the F16, for instance.  I used “longitudinal” incorrectly, but in the case of the photo, lateral is also incorrect, they provide vertical stability (yaw stability about the vertical axis).


text:
How did this plane get into this position and orientation?
taken from https://www.google.com/maps/@-33.9418465,151.174248,945m/data=!3m1!1e3
A) Landing from the east, some crosswind and touchdown off center?
B) Taking off from the east, some crosswind "
C) Landed from the south, for some reason turning left onto runway 27R, heading to international terminal "Global Exchange"?

Looks very much like a left turn to me

Option A is out of the question. This would have been a VERY late and unlikely touchdown. Option B is possible, but option C is the correct answer, especially when zooming in: https://www.google.com/maps/@-33.9413253,151.1742231,145m/data=!3m1!1e3
Judging by the tire marks on the runway (which appear to go left) this is clearly not the first aircraft (an Air China A330 if you wondered) to perform this maneuver.
The reason is clear: taxiway A2 (the high-speed exit just before the runway intersection) appears to be closed for maintenance: https://www.google.com/maps/@-33.9433411,151.17333,205m/data=!3m1!1e3
This is also evident by the following NOTAM:

Q) YMMM/QMXLC/IV/M /A /000/999/3357S15111E A) YSSY B) 18/09/21 13:00
  C) 18/09/23 19:00 D) DAILY 1300-1900 EXC SAT E) TWY A BTN TWY G AND
  TWY L NOT AVBL DUE WIP TWY A2, TWY A3, TWY A4, TWY B5, TWY B6, TWY B7
  AND TWY B9 NOT AVBL TWY B3, TWY B4, TWY K AND TWY B8 BTN RWY 16R/34L
  AND TWY B NOT AVBL TWY H BTN TWY Y AND TWY A NOT AVBL TWY J MAX 52M
  WINGSPAN TWY B BTN TWY G AND TWY B10 MAX 36M WINGSPAN REFER METHOD OF
  WORKING PLAN 17/003

Further evidence against A: no disjoint colours visible (like in https://aviation.stackexchange.com/q/52086/4108 or https://photo.stackexchange.com/questions/51998/why-does-this-satellite-image-of-an-airplane-in-motion-show-red-green-and-blue)


text:
What is dual mode adaptive landing gear system?
Referring to the NASA document Design and Development of the Blackbird:
Challenges and Lessons Learned.
On page 31, there's a mention of dual-mode adaptive landing gear, which is quoted below.

Lockheed engineers designed a dual-mode adaptive landing gear system for the YF-12A. The configuration included a strut with an optimized air load-stroke curve during landing, and an automatic switch-over system to allow for a flatter air load-stroke curve during taxi. The study demonstrated the effectiveness of a dual-mode adaptive landing gear system in reducing the dynamic response of an airplane during taxi. It also provided a database to aid in determining the degree of correlation between analytically predicted responses and actual test results with a full-scale YF-12A.63

From what I could understand, it seems it's focus was to give the landing gear loading a smoother curve and reduce the dynamic loading during taxiing, in simpler terms, dampen the minor vibrations while taxiing.
How is this type of landing gear different from the basic oleo shock struts employed today, if at all there's any difference. I mean, it pretty much does the same thing. Is there any construction difference?
An image reference would very much be appreciated.

From Testing and analysis of dual-mode adaptive landing gear, taxi mode test system for YF-12A the purpose was to obtain a very progressive rate to keep the gear from bottoming out on landing, but then move to a flatter rate to minimize ground shock when taxiing.

Two air reservoirs of differing capacity and pressure were valved to the hydraulic struts. The smaller reservoir was used for landing as it reached higher pressure faster with a given amount of fluid displaced by the compressing strut. After landing the strut was switched to the larger reservoir.
My reference provides a description of the test configuration as being similar to the actual construction, which it says is in its Reference 1 which I was unable to locate.

In any case, it is simply an additional air (now nitrogen) cylinder connected to the service port of the strut, a somewhat higher pressure is used and there is no valve since they were only testing a single mode, taxiing. The smaller reservoir is likely just the self contained strut air reservoir as in the unmodified design.
Unmodified strut

Automotive shock with reservoir to show test configuration (this was not used, it is not even a strut)

After reading this part of the document, it seems that the dual-mode is simply a two-way switchable distributor.
If you look at the image below (taken form this article) you can see a spring and a damper.

At first sight the dual-mode simply allows to switch between two stifness/damping couples, which allows to adapt the dynamic properties of the landing gear to the appropriate operation phase.
I guess some simpler manually operated (but close in principle) examples can be found on modern all-terrain bicycles with tunable suspension (e.g. here).
The picture above is related to a magnetorheological damper concept which is basically a tunable damper controlled by magnetic or electric field, which serve the same purpose.

So effectively it's just two, dampening springs one over another? Like, one can be locked out at higher speeds, while at lower speeds, both are made operational?

@Salmonbeing00, this would be my best guess indeed ! However, I think that either one or the other would be used instead of the two combined, for simplicity reasons, but I do not have any clue from the document to support this.


text:
What is the longest time after which plane crash survivors were rescued?
I found:

Aviator Bob Gauchie retains the record for solo arctic survival by a downed airman, enduring 58 days of arctic weather before his rescue in Canada 1967.
After 72 days on the glacier, 16 of the 45 people on board the crashed Uruguayan Air Force Flight 571 were rescued alive.

Any longer ?

scope: For the purpose of this question only the initial rescue from the crash site shall be considered.

Francis Gary Powers survived in a Russian prison after his plane was shot down, for 1 year 9 months and 10 days before being rescued if that counts...

thanks. I clarified the scope.

The #1 and #2 records in this category are held by Tom Hanks and Wilson. :)

At what point can we consider people are rescued? when they are spotted by rescue teams? when they are in the vehicle bringing them to an hospital? when they have been examined and doctors say "they will live"? when they leave the medical facility after intense medical treatment?

@ManuH - I'd assume when they are physically picked up by rescue teams/walk themselves to safety

@ManuH, if you find an example that breaks down the timeline in such detail please don't hesitate to post it due to concerns over when the stopwatch was clicked.

I have not found a period longer than the two you provided (quoted for completeness). It is unlikely that there is a longer period unreported, as that would be a major news item or historical note; it is possible but unverifiable there has been a person survive after a crash longer but was never rescued due to the aircraft never being recovered.

Aviator Bob Gauchie retains the record for solo arctic survival by a downed airman, enduring 58 days of arctic weather before his rescue in Canada 1967.

After 72 days on the glacier, 16 of the 45 people on board the crashed Uruguayan Air Force Flight 571 were rescued alive.

A couple notable contenders and interesting anecdotes:

Howard Snyder was shot down over Belgium during WWII and joined the Belgium resistance, staying with them for over 6 months until he was rescued by US Troops

Louis Zamperini's 47 days on the ocean after his B-24 crashed in the Pacific during WWII, likely an oceanic survival record after a plane crash, was depicted in the film and book Unbroken. Zamperini then spent another 28 months in Japanese prison camps before being repatriated

Roger Locher holds the USAF evasion record behind enemy lines, spending 23 days evading North Vietnamese troops during the Vietnam war after his F-4 was shot down

Juliane Koepecke's 11 days in the Peruvian jungle after falling from a disintegrating airplane

The record for desert survival, albeit with an unfortunate lack of rescue, the crew of Lady Be Good (WWII)

They survived for over a week in the desert with essentially no water, covering 115 miles...The remains of Moore are still lost in the Sahara’s Sand Sea of Calanscio. But he clearly broke all records for stamina and desert survival

Of the crew of the Lady Be Good, "They died trying". The best epitaph any of us could ask for.

There was a case in New Jersey in 1996 where a High school soccer team crashed in the Canadian wilderness and were presumed dead untill they were rescued 19 months later

Is this the fictional series 'yellow jackets'? https://en.wikipedia.org/wiki/Yellowjackets_(TV_series) ?

Welcome to Aviation Stack Exchange!  While we thank you for your answer, it would be greatly improved if it include supporting references.  Please [edit] so that your answer can be confirmed.


text:
Getting data from Existing ADSB Receivers
Is there any way to get data from existing ADSB receivers installed around the world?

You mean like https://www.flightradar24.com and similar sites?

Yes , i am looking for data from their adsb recievers

I don't know exactly what you want, but there are services that provide data, e.g. https://www.flightradar24.com/commercial-services/data-services

ADSB Exchange and OpenSky Network both provide access to the data they receive from their contributors.  Terms (and payment) may vary depending on whether your use is research or commercial.


text:
Is there (some form of) penetration testing in aviation?
I just listened to the first Miles to go podcast about a near miss at SFO where an Air Canada flight nearly landed on a taxiway where 4 aircrafts were waiting to take off. The incoming Air Canada flight wrongly aligned to land on the taxiway, apparently because it got confused by the lighting. Thankfully, someone noticed something was off at the last second, and the plane went around without damage.
The way I understand the podcast, it was a series of edge cases that lined up to lead to the situation. In short (please edit for accuracy if needed):
- one of the runways had its lighting off
- the aircraft had slightly old navigation equipment
- the air traffic controller was alone, and on the phone
- ...
Post incident, the inflight recorder wasn't turned off, so the critical part of the conversation was apparently recorded over, etc...
This all looks very similar to how computer security problems happen: if you input a specific value in this place at that specific moment, under this particular set of circumstances, you can get access to some confidential data.
The software industry has developed penetration testing as a method to find out such problems, where essentially you pay people to try to break into your systems, and possibly reward them every time they find a security problem. It seems like the situation above could have been identified by a similar method.
Does the aviation industry use similar practices? How does it work and what is it called? And if not, what prevents it?

This is not penetration testing, pen-testing is for finding security weaknesses, not flaws in design. Pen-testing in the software world also does not find design flaws outside of security issues. What you are asking about is human factors engineering, and yes, the airline industry has a lot of it.

@RonBeyer True. Although once pilot-less flight becomes a thing (and it will, just like driver-less cars), pen-testing will absolutely be critical for the 22nd century version of 'auto-pilot'.

@Cloud I didn't say it wasn't used at all, just what the OP is describing isn't relevant to pen testing. "Pen testing" is really going away anyway, being replaced by more encompassing paradigms being pushed by NIST. Hacking now days isn't just finding a hole, it involves many factors from social engineering to cyber security and more.

There isn't true penetration testing for the scenarios you're describing in aviation, from my understanding.  Penetration testing and cyber security is about how leniency and bugs in the system allow deliberate bad actors to compromise confidentiality, integrity, or availability (along with a few other things like privacy and non-repudiation). Typically penetration testers are limited from doing real damage and can only do things like obtain access to a restricted system or view confidential data (under strict privacy and NDA agreements).
The deliberateness is important- hackers often utilize small amounts of information gleaned or small errors to create big problems, and headline-worthy hacks involve the hacker taking full control of his target.  The basic principle is that if thousands of people are attempting to break your security, you should have a few guys on the inside testing the same thing.
The kind of scenario you're talking about is different for several reasons:

It wasn't deliberate
Testing out the scenario in the real world (to capture real issues like distracted controllers) would risk a lot more than confidential data being visible to contracted testers
There were some preventative systems which had issues and violated security assumptions like the Airport Surface Surveillance Capability system, but the bugs or ways to get around these systems don't seem to be the main factor in this incident.
This is about a potential crash, not a security issue.  It's not someone getting information they shouldn't, controlling something they shouldn't have access to, or (not really) about someone going somewhere they shouldn't.

There is risk and hazard analysis, human factors analysis, and worst-case scenario simulation, but those aren't the same as penetration testing.  While there are a small number of cases of deliberate bad actors in aviation (e.g. the Horizon plane stolen in August 2018, GermanWings Flight 9525, 9/11 attacks, etc.), and there is increasing concern for cyber security in connectivity hardware, the scenario you describe is not one of them.

There is lots of testing in aviation, in every step of the process from paper designs to an actual airframe. For situation based training the aviation industry turns to the tried and true method of
Simulation
This is similar to software in many regards (and often uses computer based simulations). Simulator tech has come a long way in the past 35 years and full motion simulators are a great way to get very very close to the real thing. If you want to test out a situation where you knock out some random approach lights, throw in low visibility and some wind shear there is no reason to risk an actual aircraft, and a pilots life. Just queue it up in the sim and see how they do.
When it comes to the physical testing of say an airframe the FAA (and other bodies) also tend to take the "...before we let it out there approach" to testing and certification. In other words before an airframe is certified for production it will undergo extensive flight testing that physically pushes the airframe and exposes it to situations it should never encounter in normal flight. Omega Tau does a great episode with an Airbus test pilot that goes deep into whats involved in this, its worth a listen.
The biggest difference in aviation is that you have control over the end to end situation. In computer security you simply cant tell people "please be careful, if you use this encryption it may break in the following cases and we dont know how to fix it". On the contrary in aviation you have the ability to train pilots and more importantly you have the ability to make (or enforce) a no-go call. If we know an approach system only works down to certain minimums you simply don't fly if the weather is below them, unlike in computer security where the system is expected to always work and always be secure and in a lot of instances, always be up.

That video of the wing testing is impressive! It seems closer to unit testing in computers, where you check that one component does what it's expected. On the system level, you point out that you have control over the entire situation, but in the above example, the pilot aligned with the wrong lights (although he clearly didn't mean to). What is the process that learns from such a mistake?

@LaurentS Unit testing is akin to testing a single part largely in isolation. If you want a computer software analog, then integration testing is closer to flight testing of an actual aircraft; it's done with mostly-finished designs, to prove that they work the way they are supposed to. Of course, that's not a perfect analog either because significant aircraft components are themselves complex systems; for example, an engine can be tested at the component level (can the fan blades take the stress?) or at the level of a completed unit (engine), but on an airplane, it's still just one component.

@LaurentS We learn that in some situations taxi lighting may appear to resemble runway lighting and we should see if this is possibly an issue. We can look at changing taxi way lights, mounts, intensity or lots of other factors. We can also look at building a more comprehensive training system for pilots that has a bigger focus on runway lighting.

The closest it comes to penetration testing would be military exercises against OPFOR equipment. This would appear lackluster compared to the pen-testing done in cyber security. Throughout the Cold War, Soviet aircraft were simulated by old and wrong Western ones, even when it was known that the substitution was inadequate.
An example of ignoring the threat model is the West's tunnel vision on X-band RF in pre-2010s design despite the Soviets extensively using C, S, L bands and IR systems, and on Soviet end, their blindness to LO technology even when it was an open secret.
In contrast, IT security pen-testing employs the tools and methods as close as possible to those used by actual threat actors, occasionally complemented by personal experience from heel-face turned black hats.
There isn't much to do pen-testing in civil aviation on, except the cockpit door locks and airport security. And each time the latter gets bypassed, it comes as a complete surprise to everyone, confirming that the principle of penetration testing is quite alien to the industry.
Pen-testing is not an effective method for preventing accidents as opposed to deliberate actions. Most accidents involve a compounding chain of small errors and bad decisions. In contrast, deliberate attacks focus on finding a short, reproducible chain of compromises that breaks the system.
Modern aviation has near-zero resistance to deliberate destructive actions by the pilots or even mechanics, or anyone with modest resources and a will to die. The aviation "pen-testing" equivalent would be for a pilot to wrestle the flight control from normal law into direct law - a much easier task than breaking into even the most vulnerable system.
On the other hand, it has very good resistant to accidents - much better than common for IT security. Defining inf-sec failure as data leaks, "accidents" would include confidential data on USB sticks, unlocked computers, passwords on post-it notes, shared accounts, documents in the trash. That's right, the norm. Not in aviation.
If aviation safety was run like IT security, planes would take an iris scan and OTP to get in, but then routinely take off with two blown tires, 3 out of 4 engines, one of them a legacy model, the PIC would go for a drink in first class right after rotation, and you'd only call ATC when you forgot your destination navpoint. Needless to say, after verifying your identity on an encrypted channel, ATC would promptly ask you in a strong Bangladesh accent to please hold and try relighting your engines.
If IT security was run like aviation safety, there would be no passwords, but each computer would only ever run job-specific software, which would have twice the learning curve of SAP R/3 with all the vowels removed.
It's not that one is worse or better - safety and security are just different.

I see the point about a deliberate destructive intent in penetration testing. I wonder though if one could play a "deliberately unlucky" pilot in a simulation, to see if this brings possible danger zones to the surface.

Regarding the "verifying your identity on an encrypted channel", there's also How do civilian pilots and ATC verify that other people on the radio are who they claim to be?

@MichaelKjörling Yep. That was really a joke in a reference to how even the most innocent things in IT get encrypted... and often turn out to be a 404 page.


text:
Why don't modern jet engines use forced exhaust mixing?
Jet engines are noisy[citation needed] - even a modern high-bypass turbofan is still deafeningly loud compared to pretty much anything except the even-louder low-bypass turbofans or a turbojet (much louder still than even a low-bypass turbofan).  Unsurprisingly, making jets quieter has been a major concern for the entire jet age; as the majority of a jet engine's noise comes from turbulence at the boundary between the hot core exhaust, on the one hand, and the ambient air (turbojets) / bypass airflow (turbofans), on the other (along with, for turbofans, a small contribution from turbulence at the boundary between the bypass airflow and the ambient air), the primary means of doing this without needing a turbine-incineratingly-high bypass ratio1 is by making it so that the two or three exhaust streams mix smoothly, and preferably do so before going out the tailpipe (so that any noise that is generated during the mixing process can be trapped within the nacelle).
To this end, early jetliners used intricate forced-mixer tailpipes, which were extremely effective at mixing the exhaust and the ambient air, and, thereby, reducing noise; they could either be built into the engine at manufacture time, or retrofitted later on as a "hushkit".  These could be seen both on turbojets...2

...and on turbofans.3

With the switch to high-bypass turbofans in the 1970s and 1980s, the dramatically-increased bypass ratio of the new engines was enough all by itself to produce a large drop in noisiness, such that even a plain, unmixed tailpipe was acceptable, and the forced-mixer tailpipes of the earlier engines slowly disappeared from view as the numbers of aircraft using the older engines dwindled.
However, since then, the NIMBYs have gotten more exacting and noise standards have continued to grow stricter and stricter, forcing jets to again use exhaust mixing to make them quieter.  Two methods for doing this are in common use:
Chevrons
These sawtoothed tailpipe rims enhance the mixing of the core, bypass, and ambient air, reducing noise:4

Shared tailpipes
These engines simply send both the core and bypass airflow through a single, long tailpipe, where shearing forces at the boundary between the two airstreams create turbulence that causes them to mix to some extent before exiting the engine:5

Both of these methods, however, are fairly inefficient at mixing the different airstreams; a scaled-up forced mixer would be far more mixy (and, therefore, more noise-reducingy).  So why do modern high-bypass turbofans still use inefficient methods of exhaust mixing, instead of the more effective forced mixing?

1: A higher bypass ratio requires (for a given thrust rating) more power per unit turbine, which requires the turbine to run hotter.
2: Exhaust mixer of a General Electric CJ805-3 turbojet from a Convair 880 (image by Thomas R. Machnitzki, via DoxTxob at Wikimedia Commons).
3: Exhaust mixer of a Rolls-Royce Conway RCo.12 low-bypass turbofan from a Boeing 707-420 (image by Alf van Beem at Wikimedia Commons).
4: Exhaust mixer of a General Electric GEnx-2B high-bypass turbofan from a Boeing 747-8I (image by Olivier Cleynen at Wikimedia Commons); note the chevrons on both the fan cowling (here opened to appease the peanut gallery), for mixing the bypass airflow with the ambient air, and on the core tailpipe, for mixing the core exhaust with the bypass airflow.
5: Exhaust mixers of two General Electric/SNECMA CFM56-5C high-bypass turbofans from an Airbus A340-300 (image by Hansueli Krapf at Wikimedia Commons); two more A340s, along with their engines and said engines' exhaust mixers, are also visible in the background (one each at upper left and upper far right; please ignore the 747 at upper mid right).

I commend your use of examples and sources!

I might push back a bit on the term NIMBY. :-) I love airplanes (I'm here, aren't I?), but when an A380 is at full throttle ~3000 feet right above your head (according to FlightRadar24), it's looooud. Even with smaller jets, it definitely gets a bit old to have them taking off over your head every couple minutes.

The last paragraph ("fairly inefficient") - [citation needed]. They normally do have mixers inside, even if smaller ones.

“Jet engines are noisy[citation needed]” is the funniest thing I’ve read all day…

Why don't modern jet engines use forced exhaust mixing?

Because there isn't as much gain to be achieved from the jet exhaust any more, and because forced mixing impacts performance.

Gains. From The Jet Engine by Rolls Royce. The text in the lower right corner reads:

A comparison of the noise distribution of two generations of engines. The bubbles approximately indicate the relative size of the main individual engine noise sources and the angular extent indicates where each is most prominent. The noise contributions from a modern turbofan engine are greatly reduced and much more evenly matched than from a turbojet.

On the left the noise footprint of a typical 1960s engine where by far most of the noise was caused by the jet exhaust. This is where most of the thrust came from - the exhaust exits at Mach 1, at 700 °C over 600 m/s. Huge gains are to be made in slowing this down.
On the right a 1990s generation engine, where the dominant noise source is the fan - this is now where most gains can be made. The jet takes third place, Turbine + combustion is slightly higher. The overall noise level is significantly lower, since the ear perceives noise logarithmically: two noise sources of 100 dB add up to 103 dB.

Performance impact. From the Wikipedia page linked by the OP:

Hush kits can adversely affect the range and performance of the aircraft they are fitted to because of the extra weight. It also reduces engine performance and aerodynamic efficiency.

The exhaust mixing kit catches some of the generated thrust through friction and back pressure, and is therefore always a performance reducer. The Wikipedia page mentions an increase reduction in fuel burn of 0.5% for short trips of the Boeing 727.

This fits with common experience, also.  Anyone who has been to an airshow or has seen military jets flying can attest that naked turbojets can be painfully loud.  On a modern passenger jet with high-bypass engines the biggest thing you really hear is fan and turbine noise - that deafening, roaring crackle, characteristic of turbojets, is so heavily muted that you don't really pay it much attention.

@J... It was very apparent in an office at Amsterdam airport, where the noise of jets taking off was just part of the background until a 727 or BAC-111 would take off. A rare occurrence fortunately, but startled everyone because of the deafening noise of the turbojets. Even the hush kitted ones were pretty loud and left a trail of sooty smoke.

@Koyovis: Those aren't turbojets, but low-bypass turbofans, which are indeed much louder than modern high-bypass turbofans.

Also, please provide a link to the page from where you got that image.

It's on slideshare.net


text:
Why are piston-engined aircraft generally exempted from U.S. flight recorder requirements?
Most, if not all, of the FAA’s requirements for carriage of flight recorders do not apply to piston-engined aircraft.
For instance, 14 CFR 91.609(c)(1) (emphasis added):

No person may operate a U.S. civil registered, multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration, excluding any pilot seats of 10 or more [sic] that has been manufactured after October 11, 1991, unless it is equipped with one or more approved flight recorders...

and 14 CFR 91.609(e):

...after October 11, 1991, no person may operate a U.S. civil registered multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of six passengers or more and for which two pilots are required by type certification or operating rule unless it is equipped with an approved cockpit voice recorder...

Even the NTSB’s repeated recommendations that the FAA require the general carriage of flight recorders still exclude piston-engined aircraft from this requirement; for instance, recommendations A-09-10 (emphasis added):

Require all existing turbine-powered, nonexperimental, nonrestricted-category [sic] aircraft that are not equipped with a cockpit voice recorder and are operating under 14 Code of Federal Regulations Parts 91, 121, or 135 to be retrofitted with a crash-resistant flight recorder system.  [...]

A-13-12:

Require the installation of a crash-resistant flight recorder system on all newly manufactured turbine-powered, nonexperimental, nonrestricted-category [sic] aircraft that are not equipped with a flight data recorder and a cockpit voice recorder and are operating under 14 Code of Federal Regulations Parts 91, 121, or 135.  [...]

and A-13-13:

Require all existing turbine-powered, nonexperimental, nonrestricted-category [sic] aircraft that are not equipped with a flight data recorder or cockpit voice recorder and are operating under 14 Code of Federal Regulations Parts 91, 121, or 135 to be retrofitted with a crash-resistant flight recorder system.  [...]

I can’t see any objective reason why an aircraft would magically have less need to carry flight recorders just because its engine happens to use thrusting pistons instead of a gas turbine - especially since turboprop aircraft are (mostly) required to carry flight recorders, and turboprop aircraft, other than having turbine-driven propellers, are little different from piston-engined aircraft (indeed, many turboprop aircraft are piston-engined aircraft whose piston engines have been replaced with turboprops).
If anything, it would seem that piston-engined aircraft would have a greater need for flight recorders, for a couple of reasons:

Piston engines are orders of magnitude more prone to breaking down in midair than turbine engines are, making aircraft that use them more likely to crash (at least from engine failures), and, thus, more likely to generate an accident investigation, for which flight recorders are extremely valuable (this is, after all, their original and primary purpose).
Large piston-engined aircraft are also generally considerably older than the vast majority of comparable jet and turboprop aircraft, for the simple reason that few if any manufacturers still produce large piston aircraft rather than jets or turboprops.  Older aircraft, for a multitude of obvious reasons, are more vulnerable to crash-inducing malfunctions or failures than newer aircraft, and are also more likely to lack many of the safeguards built into newer aircraft; yet, a 70-year-old DC-3 that’s falling apart at the seams is not required to carry any sort of flight recorder, even in scheduled airline service, so long as it isn’t retrofitted with turboprop engines, while a brand-new Twin Otter doing exactly the same job is, for the sole reason that its propellers are turbine-driven.
The vast majority of piston-engined aircraft are smaller general-aviation types, which are much more likely than large commercial aircraft to be piloted by people lacking a high degree of competence, or people in possession of a high degree of sloppiness, or habitual rule-breakers, or people with another reason they probably shouldn’t be flying; conversely, the vast majority of general-aviation aircraft are piston-engined, and, thus, even if every single U.S.-registered turbine aircraft were required to carry flight recorders, there would be little benefit for the general-aviation community.  In contrast, nearly all long-haul passenger airliners, and most shorter-haul ones as well, are jet-powered, while the remainder (primarily feeder and commuter aircraft making short, low hops) overwhelmingly use turboprop engines; most large freighters are also jets (with some turboprops thrown in), while smaller freighters are primarily turboprops and smaller jets; and business jets (as the name indicates) use jet engines, while most corporate propeller aircraft use turboprops.  Airline (both passenger and cargo) and corporate pilots are held to much stricter standards than a guy going sightseeing in his C-172, and, not coincidentally, crash far less often than general-aviation pilots do (and, even if airline and general-aviation pilots had exactly the same numbers of crashes per unit airtime, there would still be more general-aviation crashes than airliner crashes, for the simple reason that there are far more general-aviation aircraft, pilots to fly said aircraft, and flights made by said pilots in said aircraft, than is the case for airliners); thus, requiring turbine aircraft, but not piston aircraft, to carry flight recorders still leaves the vast majority of crashed flights flight-unrecorded.

Why do U.S. flight-recorder requirements, and recommendations and proposals for same, exempt piston-engined aircraft for no discernible reason?

I think you answered your own question: “Airline (both passenger and cargo) and corporate pilots are held to much stricter standards than a guy going sightseeing in his C-172”. There’s no obvious reason why private vehicles - which is what most GA aircraft are - should require constant monitoring and recording. By analogy, I imagine that many people would favor recorders in buses and trains, but might also hesitate to put one in their own car.

Yes, small piston craft crash more often, but those crashes kill far fewer people each, and in nearly all cases the cause is obvious, so a CVR or FDR would be superfluous.

Plus it would be onerous on owners to retrofit a system in.  Look at how long it has taken to get ADS-B Out installed into all planes that need it, and that's with a $500 rebate too. As Jan 1 2020 approaches, prices seem to have gone down and the options to have gone up, some as simple as replacing a wing /strobe, or the tail position light, with a new unit containing a light/strobe/GPS receiver/ADS-B transmitter.

@Pondlife StephenS CrossRoads: Then why not specifically exempt general-aviation aircraft (thus avoiding placing turboprop GA aircraft at a disadvantage relative to their piston-powered pals, while simultaneously eliminating the loophole that allows non-GA piston-engine aircraft to skate by without flight recorders), rather than piston-engined aircraft (which aren't all GA aircraft, and don't comprise the entirety of the GA aircraft population anyways)?

GA covers such a broad spectrum of aviation that it's hard to imagine a single rule working for all of them. It's like any "why don't we have..." question in aviation: cost vs benefit. Are the financial, electrical, weight and privacy costs of putting flight recorders in all aircraft - and the numerous engine, fuel and control surface sensors they need - worth the benefit of the information that's recovered from them? FWIW, modern avionics increasingly provide a lot of information to investigators, even in piston aircraft.

"Multi-engine, turbine-engined" is basically FAA's shorthand for "large aircraft".
That is that way, because of the economics of such a craft.
If somebody figured out how to economically build a short-haul airliner (Dash-8 or Bae146 sized) that was entirely piston-engine powered, FAA would rewrite the rule to include that type.

That also aligns with their desire not to "overburden with regulations" the very old DC-3/4/5/6/7, Commando, Caribou, CL-215, etc. still flying in waterbomber service (CalFire etc.), bush airline service (Buffalo),  or airshow/heritage fleets.  These are services that would simply fold up if pressed with the full weight of modern airliner regulations.
The Federal Railroad administration does a similar thing with heritage railways, broadly exempting them from the picayune detail imposed on Amtrak etc.
And of course FAA has never sought to impose commercial rules on GA hobbyists of modest means, who might happen to have a Skymaster or Twin Beech.

I think you mean the CL-215 not the CL-415.


text:
What problems can be encountered if an airplane does not undergo wind tunnel testing?
SpaceShipOne did not use any wind tunnel testing. According to the Scaled Composites FAQs:

Q: Did you do wind tunnel testing?
A: No. All design refinements and performance predictions have been derived from Computational Fluid Dynamic tools.

What problems would such an aircraft face (which is designed completely without wind tunnel testing)?

You could crash and die due to an effect your computer modelling failed to account for.

For decades, there was no wind tunnel testing performed. There will be, of course, more unknowns about performance and flight characteristics, but with modern computer simulation technology those can be greatly reduced.


text:
What are the different kinds of de-ice fluid?
When frost adheres to the airplane or it is snowing, you need to make sure the airplane is clean when you depart.  You've probably seen the trucks spraying aircraft in the winter before departure, but what are the spraying it with?
I know of at least 4 types of de-/anti-ice fluids but perhaps there are others.  What does each fluid consist of and what is its function?  How do I know if these fluids are available at an airport I plan to operate from?  Are there limits in how soon I must depart once fluid is applied?

Fluid Types
Wikipedia contains a good summary of the different types of fluid:

Types

Type I fluids have a low viscosity, and are considered "unthickened". They provide only short term protection because they
  quickly flow off surfaces after use. They are typically sprayed on hot
  (130–180°F, 55-80°C) at high pressure to remove snow, ice, and frost.
  Usually they are dyed orange to aid in identification and application.
Type II fluids are pseudoplastic, which means they contain a polymeric thickening agent to prevent their immediate flow off
  aircraft surfaces. Typically the fluid film will remain in place until
  the aircraft attains 100 knots or so (almost 200 km/h), at which point
  the viscosity breaks down due to shear stress. The high speeds
  required for viscosity breakdown means that this type of fluid is
  useful only for larger aircraft. The use of type II fluids is
  diminishing in favour of type IV. Type II fluids are generally light
  yellow in color.
Type III fluids can be thought of as a compromise between type I and type II fluids. They are intended for use on slower aircraft, with
  a rotation speed of less than 100 knots. Type III fluids are generally
  light yellow in color.
Type IV fluids meet the same AMS standards as type II fluids, but they provide a longer holdover time. They are typically dyed green to
  aid in the application of a consistent layer of fluid.

Chemical Composition
The main component of deicing fluid is usually propylene glycol or
  ethylene glycol. Other ingredients vary depending on the manufacturer,
  but the exact composition of a particular brand of fluid is generally
  held as confidential proprietary information.

Call ahead to the airport to see what kind of deice/anti-ice fluid that they have because each one is different.
Time Limits
Every year, the FAA publishes tables which include information about how long the various deice fluids will provide protection under various weather conditions.  Here is an example table:

For this particular fluid (ABAX ECOWING AD-49 Type IV) we can lookup a specific example such as:

-10 Degrees Celcius
75% fluid and 25% water
Light Snow

This shows that the fluid will provide protection for 1:40 to 2:05. If you are delayed longer than that, you will need to deice again.  Since every part of the aircraft needs to be protected, the timing starts when they first start spraying the aircraft.  Note that other types of fluid (particularly Type I fluids) have much shorter holdover times than this, so be careful and make sure that you check!

Resources

OFFICIAL FAA HOLDOVER TIME TABLES WINTER 2013-2014
AC 120-60B - Ground Deicing and Anti-icing Program


text:
Is locking the cockpit door from inside is a normal procedure when one pilot leaves?
When a pilot leaves the cockpit to go to the toilet should the second pilot lock the door?
For me it's mandatory in case of the other pilot is taking in hostage and is forced to tap the code.
So can the pilot still in the cockpit can have locked the door and then lose consciousness?
Imagine the pilot goes to toilet and a problem occurs, the plane start to stall for example, and he can't reach the cockpit leaving the other alone to manage the situation.
For me the only situation is 3 pilots or never let him goes outside in small trip.

Yes, the door is locked (usually at all times during flight and opened only when a pilot needs to enter or exit the flight deck.) The rest of what you ask is covered in this question.

I'm voting to close this question as a duplicate because it already has an answer here: http://aviation.stackexchange.com/q/13566/755 .

@reirab I agree these questions are closely related, but they aren't the same. This one asks "is it normal procedure?", the other one asks "how can you open the door from outside?".

@Pondlife Nevertheless, its answer is included in the other one.

For most modern, large commercial passenger planes, there is an automatic lock, which then requires the PNF (Pilot Not Flying and outside of the cockpit) to enter an unlock code, or more usually, for the PF (Pilot Flying, and hopefully inside the cockpit) to remotely unlock the door.
The emergency access code typically sounds a cockpit warning buzzer and has a delayed operation, allowing the PF to override this in case of an unwanted, erm, "visitor", yet at the same time, allowing access to the PNF in case of PF incapacitation.
Commercially, three pilots (or two pilots and a flight engineer) on each flight are no longer economically viable for almost all airlines.  Indeed, most couldn't host a third person comfortably for the whole flight - jump seats are fine for short bursts, but not for a long-haul flight, for example.
Therefore, most airlines are now adapting their cockpit manning procedures to ensure another member of the flight crew (typically a flight attendant) joins the PF before the PNF leaves the cockpit.

The details of how the door locking system works is described in this question. It explains that if the pilot inside loses consciousness then the pilot in the cabin can open the door after a delay.
European airlines are putting regulations in place to ensure a pilot is never alone in the cockpit to avoid a repeat of the recent crash. This means calling in a flight attendant to the cockpit while the pilot is on the toilet.

This is very relevant, but it doesn't answer the question about whether it's "normal procedure" to lock the door or not when only one pilot is in the cockpit. Admittedly, the OP bundled two questions into one, which doesn't help!